Merge #1266

1266: Make TyTy::BaseType::destructure recursive r=philberty a=philberty

In the case of Generic Associated Types we end up

  placeholders->projections->generic-param->i32

This means we need to keep destructuring the TyTy object until we finally
get the real type at the end. In order to do this safely we need to ensure
we add in recursion limits and apply this where it matters such as
compiling types in general too.


Co-authored-by: Philip Herron <philip.herron@embecosm.com>

4 files changed, 54 insertions, 31 deletions

diff --git a/gcc/rust/backend/rust-compile-type.cc b/gcc/rust/backend/rust-compile-type.cc
index 3874027..102bc0a 100644
--- a/gcc/rust/backend/rust-compile-type.cc
+++ b/gcc/rust/backend/rust-compile-type.cc
@@ -112,9 +112,15 @@ TyTyResolveCompile::visit (const TyTy::PlaceholderType &type)
 void
 TyTyResolveCompile::visit (const TyTy::ParamType &param)
 {
-  // FIXME make this reuse the same machinery from constexpr code
-  recursion_count++;
-  rust_assert (recursion_count < kDefaultRecusionLimit);
+  if (recurisve_ops++ >= rust_max_recursion_depth)
+    {
+      rust_error_at (Location (),
+		     "%<recursion depth%> count exceeds limit of %i (use "
+		     "%<frust-max-recursion-depth=%> to increase the limit)",
+		     rust_max_recursion_depth);
+      translated = error_mark_node;
+      return;
+    }
 
   param.resolve ()->accept_vis (*this);
 }
diff --git a/gcc/rust/backend/rust-compile-type.h b/gcc/rust/backend/rust-compile-type.h
index 3e1f903..262b8fc 100644
--- a/gcc/rust/backend/rust-compile-type.h
+++ b/gcc/rust/backend/rust-compile-type.h
@@ -63,16 +63,13 @@ public:
 private:
   TyTyResolveCompile (Context *ctx, bool trait_object_mode)
     : ctx (ctx), trait_object_mode (trait_object_mode),
-      translated (error_mark_node), recursion_count (0)
+      translated (error_mark_node), recurisve_ops (0)
   {}
 
   Context *ctx;
   bool trait_object_mode;
   tree translated;
-
-  // FIXME this needs to be derived from the gcc config option
-  size_t recursion_count;
-  static const size_t kDefaultRecusionLimit = 5;
+  int recurisve_ops;
 };
 
 } // namespace Compile
diff --git a/gcc/rust/lang.opt b/gcc/rust/lang.opt
index a6dabbf..58ec9a7 100644
--- a/gcc/rust/lang.opt
+++ b/gcc/rust/lang.opt
@@ -66,6 +66,10 @@ frust-dump-
 Rust Joined RejectNegative
 -frust-dump-<type>	Dump Rust frontend internal information.
 
+frust-max-recursion-depth=
+Rust RejectNegative Type(int) Var(rust_max_recursion_depth) Init(64)
+-frust-max-recursion-depth=integer
+
 frust-mangling=
 Rust Joined RejectNegative Enum(frust_mangling) Var(flag_rust_mangling)
 -frust-mangling=[legacy|v0]     Choose which version to use for name mangling
diff --git a/gcc/rust/typecheck/rust-tyty.cc b/gcc/rust/typecheck/rust-tyty.cc
index d0e8b76..f03bc82 100644
--- a/gcc/rust/typecheck/rust-tyty.cc
+++ b/gcc/rust/typecheck/rust-tyty.cc
@@ -252,33 +252,49 @@ BaseType::get_root () const
 const BaseType *
 BaseType::destructure () const
 {
-  switch (get_kind ())
+  int recurisve_ops = 0;
+  const BaseType *x = this;
+  while (true)
     {
-      case TyTy::TypeKind::PARAM: {
-	const TyTy::ParamType *p = static_cast<const TyTy::ParamType *> (this);
-	return p->resolve ();
-      }
-      break;
-
-      case TyTy::TypeKind::PLACEHOLDER: {
-	const TyTy::PlaceholderType *p
-	  = static_cast<const TyTy::PlaceholderType *> (this);
-	rust_assert (p->can_resolve ());
-	return p->resolve ();
-      }
-      break;
-
-      case TyTy::TypeKind::PROJECTION: {
-	const TyTy::ProjectionType *p
-	  = static_cast<const TyTy::ProjectionType *> (this);
-	return p->get ();
-      }
+      if (recurisve_ops++ >= rust_max_recursion_depth)
+	{
+	  rust_error_at (
+	    Location (),
+	    "%<recursion depth%> count exceeds limit of %i (use "
+	    "%<frust-max-recursion-depth=%> to increase the limit)",
+	    rust_max_recursion_depth);
+	  return new ErrorType (get_ref ());
+	}
 
-    default:
-      return this;
+      switch (x->get_kind ())
+	{
+	  case TyTy::TypeKind::PARAM: {
+	    const TyTy::ParamType *p = static_cast<const TyTy::ParamType *> (x);
+	    x = p->resolve ();
+	  }
+	  break;
+
+	  case TyTy::TypeKind::PLACEHOLDER: {
+	    const TyTy::PlaceholderType *p
+	      = static_cast<const TyTy::PlaceholderType *> (x);
+	    rust_assert (p->can_resolve ());
+	    x = p->resolve ();
+	  }
+	  break;
+
+	  case TyTy::TypeKind::PROJECTION: {
+	    const TyTy::ProjectionType *p
+	      = static_cast<const TyTy::ProjectionType *> (x);
+	    x = p->get ();
+	  }
+	  break;
+
+	default:
+	  return x;
+	}
     }
 
-  return this;
+  return x;
 }
 
 TyVar::TyVar (HirId ref) : ref (ref)